Spectrophotometers for the Measurement of Light in Polar Ice and Snow

Abstract

Two portable spectrophotometers have been designed to record light scattering and absorption in polar ice and snow. In the first instrument optical fibers are used to transmit light from the interior of the ice to the spectrophotometer. Such an arrangement allows light measurements up to 2 m away from the instrumentation with minimal disturbance of the natural environment. A miniaturized, submersible spectrophotometer was also built for in situ measurements under floating sea ice. This version, except for the recording apparatus, is entirely self-contained and is housed in a cylindrical tube 9 cm in diameter and 60 cm in length. The unit can be lowered into the ocean through a small borehole in the ice; position and orientation are controlled from the surface. Both spectrophotometers are designed to measure light intensities in the visible spectrum (400-1000 nm). Wavelength resolution is adjustable down to 8 nm at a wavelength of 400 nm, with a field of view of less than 3 degrees . Sensitivities in the pr sent versions are sufficient for measurements through several meters of sea ice with a relative accuracy of 1%. Instrument operation has been tested in the Arctic down to temperatures of -25 degrees C.